Apparatus and method for degrading a web in the machine direction while preserving cross-machine direction strength

ABSTRACT

An embossing system is provided for embossing a web having a first embossing roll having embossing elements and a second embossing roll having embossing elements, wherein at least a portion of the embossing elements of the first and second embossing rolls are substantially oriented in the cross-machine direction. The embossing roll may be crowned, may have alignment means, and may be provided with precision gearing.

CONTINUING DATA

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/036,770, filed Dec. 21, 2001.

The present invention relates to an apparatus and method for embossing amoving web of material, such as paper, to create a functional controlleddegradation of the machine direction strength of the web while limitingdegradation of the cross-machine direction strength of the web. In oneembodiment, the present invention relates to an apparatus and method forembossing a moving web using an embossing system having perforateembossing elements oriented to define perforating nips substantiallyoriented in the cross-machine direction to improve the flexibility,feel, bulk, and absorbency of the paper. In another embodiment, thepresent invention relates to an apparatus and method for embossing amoving web using an embossing system having embossing elements orientedto define perforating nips substantially oriented in the cross-machinedirection to improve the flexibility, feel, bulk, and absorbency of thepaper, while reducing circumferential alignment drift of the embossingrolls in the machine direction and reducing the possibility of a caliperprofile. In addition, the invention relates to an apparatus and methodof aligning embossing rolls having cross-machine direction embossingelements to attain engagement.

Embossing is the act of mechanically working a substrate to cause thesubstrate to conform under pressure to the depths and contours of apatterned embossing roll. Generally the web is passed between a pair ofembossing rolls that, under pressure, form contours within the surfaceof the web. During an embossing process, the roll pattern is impartedonto the web at a certain pressure and/or penetration. In perforateembossing the embossing elements are configured such that at least aportion of the web located between the embossing elements is perforated.As used herein, generally, “perforated” refers to the existence ofeither (1) a macro-scale through aperture in the web or (2) when amacro-scale through aperture does not exist, at least incipient tearingsuch as would increase the transmittivity of light through a smallregion of the web or would decrease the machine direction strength of aweb by at least 15% for a given range of embossing depths.

Embossing is commonly used to modify the properties of a web to make afinal product produced from that web more appealing to the consumer. Forexample, embossing a web can improve the softness, absorbency, and bulkof the final product. Embossing can also be used to impart an appealingpattern to a final product.

Embossing is carried out by passing a web between two or more embossingrolls, at least one of which carries the desired emboss pattern. Knownembossing configurations include rigid-to-resilient embossing andrigid-to-rigid embossing.

In a rigid-to-resilient embossing system, a single or multi-plysubstrate is passed through a nip formed between a roll whosesubstantially rigid surface contains the embossing pattern as amultiplicity of protuberances and/or depressions arranged in anaesthetically-pleasing manner, and a second roll, whose substantiallyresilient surface can be either smooth or also contain a multiplicity ofprotuberances and/or depressions which cooperate with the rigid surfacedpatterned roll. Commonly, rigid rolls are formed with a steel body whichis either directly engraved upon or which can contain a hardrubber-covered, or other suitable polymer, surface (directly coated orsleeved) upon which the embossing pattern is formed by any convenientmethod such as, for example, being laser engraved. The resilient rollmay consist of a steel core provided with a resilient surface, such asbeing directly covered or sleeved with a resilient material such asrubber, or other suitable polymer. The rubber coating may be eithersmooth or engraved with a pattern. The pattern on the resilient roll maybe either a mated or a non-mated pattern with respect to the patterncarried on the rigid roll.

In the rigid-to-rigid embossing process, a single-ply or multi-plysubstrate is passed through a nip formed between two substantially rigidrolls. The surfaces of both rolls contain the pattern to be embossed asa multiplicity of protuberances and/or depressions arranged into anaesthetically-pleasing manner where the protuberances and/or depressionsin the second roll cooperate with those patterned in the first rigidroll. The first rigid roll may be formed, for example, with a steel bodywhich is either directly engraved upon or which can contain a hardrubber-covered, or other suitable polymer, surface (directly coated orsleeved) upon which the embossing pattern is engraved by anyconventional method, such as by laser engraving. The second rigid rollcan be formed with a steel body or can contain a hard rubber covered, orother suitable polymer, surface (directly coated or sleeved) upon whichany convenient pattern, such as a matching or mated pattern, isconventionally engraved or laser-engraved. In perforate embossing, arigid-to-rigid embossing system is typically used. However, arigid-resilient configuration can also be-used for perforate embossing.

When substantially rectangular embossing elements have been employed inperforate embossing, the embossing elements on the embossing rolls havegenerally been oriented so that the long direction axis, i.e., the majoraxis, of the elements is in the machine direction. That is, the majoraxis of the elements is oriented to correspond to the direction of therunning web being embossed. These elements are referred to as machinedirection elements. As a result, the elements produce perforations whichextend primarily in the machine direction and undesirably decrease thestrength of the web in the cross-machine direction. This orientationimproves absorbency and softness, but can degrade, i.e., reduce thestrength of, the web primarily in the cross-machine direction while lesssignificantly degrading the strength of the web in the machinedirection. As a result, the tensile strength of the web in thecross-machine direction is reduced relatively more, on a percentagebasis, than that of the machine direction. In addition, thecross-machine direction strength of the base sheet is typically lessthan that of the machine direction strength. As a result, by embossingwith machine direction elements, the cross-machine direction strength iseven further weakened and, accordingly, because the finished productwill fail in the weakest direction, the product will be more likely tofail when stressed in the cross-machine direction. Often, it ispreferred that the web is “square,” i.e., has a machinedirection/cross-machine direction tensile ratio close to 1.0.

Cross-machine direction tensile strength can be associated with consumerpreference for paper toweling. In particular, consumers prefer a strongtowel, of which cross-machine direction and machine direction strengthare two components. Because the un-embossed base sheet is typically muchstronger in the machine direction than the cross-machine direction, aprocess is desired which results in both improved absorbency andsoftness without sustaining excessive losses in cross-machine directiontensile strength.

U.S. patent application Ser. No. 10/036,770, addressed at least theabove described problem by providing at least two embossing rolls,wherein at least a portion of the elements are oriented to provideperforating nips which are substantially in the cross-machine directionand are configured to perforate the web, thereby allowing relativelygreater degradation, i.e., a reduction of strength, of the web in themachine direction while preserving more of the cross-machine directionstrength. It was observed, however, that at times in operation of theabove invention the circumferential alignment of the embossing rollstended to drift in the machine direction. Such drifting could possiblylead to interference between the adjacent engaging embossing elements ofthe embossing rolls which could cause unwanted degradation of the paperweb and, ultimately, could lead to damage or destruction of the elementsthemselves. In addition, the drifting could lead to a non-uniform finalproduct.

It has been discovered that the machine direction drifting is caused, atleast in large part, by the gearing commonly used on embossing rolls. Instandard gearing mechanisms, the gears are constructed by first formingthe gears out of metal block. To achieve the hardness levels requiredfor operating conditions, the gears are then heat treated. The heattreating process typically causes deformation in the gears and,therefore, the gears lack the necessary precision for certainapplications. When machine direction elements alone are used, in somecases, this lack of precision may be acceptable because, as noted above,the drift is in the machine direction. Thus, in those cases, thecircumferential alignment drift will only lead to a change in theembossing pattern, but will not lead to interference of the embossingelements. When perforate embossing a paper web with cross-machinedirection elements, on the other hand, the circumferential alignmentdrift can lead to interference between the elements.

The present invention addresses at least embossing roll circumferentialalignment drift by providing a cross-machine embossing system withoutcircumferential drift by providing a precision gearing system for usewith the cross-machine direction element embossing rolls. In particular,the present invention addresses at least embossing roll circumferentialalignment drift by providing a precision gearing system that willsubstantially prevent the embossing rolls from shiftingcircumferentially with respect to one another in the machine directionas a web is perforate embossed. According to one embodiment of thepresent invention, the gears are constructed by first heat treating ametal base material to achieve the desired hardness. The base materialis then hobbed to form the gear structure. In addition, precision hubsare provided to maintain the concentricity of the embossing roll gears.In particular, conventional hubs and bushings are formed separately.When the bushings are press-fit between the hub and the journal,distortion of the hub can occur, thereby potentially changing theconcentricity of the hub. In the current invention, the hub and bushingare machined together after the bushing is press-fitted between the huband an arbor. Because the press-fitting takes place before themachining, any distortion is significantly reduced or eliminated and theconcentricity of the hub is maintained.

In addition to the above, the initial alignment for engagement of thecross-machine direction element embossing rolls can be time consuming.Alignment is important because if the rolls are improperly aligned theopposing elements can come into contact with one another, causing damageto the elements. In traditional embossing rolls having machine directionelements, alignment can be accomplished with less difficulty because theoperator aligning the rolls can visually see the alignment of theelements. When the embossing elements are oriented in the cross-machinedirection, on the other hand, the operator does not generally have thevisual access necessary to align the rolls.

One alignment process according to the invention is described asfollows. First, the operator brings the rolls into close proximity,without allowing the elements to contact. A web, such as a nipimpression paper, is then fed through the embossing roll, leaving animprint of the location of the elements on the web. The imprinted web isanalyzed to determine whether the elements will contact each other whenbrought into closer proximity. Based on the outcome of the imprint, themachine direction alignment of the embossing rolls may be adjusted.After any necessary adjustment, the embossing rolls are brought intocloser proximity and a web, such as a nip impression paper, is onceagain fed through the embossing rolls to determine the relative locationor proximity of the elements. This process is repeated until theembossing rolls are in operating position. In addition, anytime one orboth of the rolls are removed for servicing, or the circumferentialalignment is changed for any reason, the alignment process must berepeated. Using this method, aligning the rolls can be very timeconsuming. Those of ordinary skill in the art will understand that anyprocess which achieves the necessary alignment can be used.

A reduction in alignment time is addressed by providing an alignmentsystem on the embossing rolls. In one embodiment according to thepresent invention, an adjustable collar ring is provided on the firstembossing roll. The second embossing roll may have an adjustable collarring, a fixed collar ring, a machined keyway, or other structure thatwill permit the alignment with the first embossing roll. The collars arepositioned such that when aligned and the emboss rolls are engaged, theembossing elements will not interfere with one another. A key may beprovided for alignment of the collars. In another embodiment of thepresent invention, scribe marks are provided on each of the first andsecond embossing rolls.

It has been discovered that when perforating a web in the cross-machinedirection a caliper profile can exist. In particular, when perforating aweb in, the cross-machine direction at operating speeds, in someinstances the caliper of the perforated web near the ends of theembossing rolls can be greater than that at the middle of the roll. Thiscaliper profile indicates that a higher degree of perforation wasaccomplished near the ends of the embossing rolls. It is believed thatthis profile is a function of the speed of the web as it is perforateddue to deflection of the embossing rolls. While deflection also occurswhen embossing with elements creating perforations in the machinedirection, the deflection seems to be aggravated when embossing tocreate perforations extending in the cross-machine direction.

The present invention addresses caliper profile by providing at leastone crowned embossing roll. In one embodiment two crowned rolls areused. A roll is crowned when the diameter of the center portion of theembossing roll is greater than that at the ends. The roll may be crownedby gradually reducing the diameter of the embossing roll when movingfrom the center portion of the embossing roll towards the ends of theembossing roll. In another embodiment, the reduction towards the ends ofthe roll is increased such that the shape of the crown is generallyparabolic. In yet another embodiment, the reduction of the roll diameterexists only at the ends of the roll. In still yet another embodiment,the reduction of the roll diameter is a stepped reduction.

Further advantages of the invention will be set forth in part in thedescription which follows and in part will be apparent from thedescription or may be learned by practice of the invention. Theadvantages of the invention may be realized and attained by means of theinstrumentalities and combinations particularly pointed out in theappended claims.

SUMMARY OF THE INVENTION

As embodied and broadly described herein, the invention includes anembossing system for embossing and perforating at least a portion of aweb comprising a first embossing roll having embossing elements and atleast a second embossing roll having embossing elements, whereinjuxtaposition and engagement of the first and second embossing rollsdefine a plurality of perforate nips for embossing and perforating theweb and wherein at least a predominate number of the embossing elementsare configured so as to produce perforating nips which are substantiallyoriented in the cross-machine direction. In one embodiment, theinvention further includes an embossing system wherein substantially allof the embossing elements of the first and second embossing rollsproduce perforating nips which are substantially oriented in thecross-machine direction. Further, in one embodiment, the cross-machineembossing elements are at an angle of 85 to 95° from the machinedirection, which is equivalent to having a skew of ±5°.

In another embodiment, the invention includes an embossing system forembossing at least a portion of a web comprising a first embossing rolland at least a second embossing roll, wherein each of the first andsecond embossing rolls has at least one juxtaposable embossing elementcapable of producing a perforating nip substantially oriented in thecross-machine direction, thereby defining a cross-machine directionperforate nip between the cross-machine direction elements for embossingand perforating the web, and wherein at least a substantial portion ofthe cross-machine direction elements have at least the ends beveled.

In yet another embodiment, the invention includes an embossing systemfor embossing and perforating at least a portion of a web comprising afirst embossing roll and at least a second embossing roll, wherein eachof the first and second embossing rolls has at least one juxtaposableelement capable of producing a perforating nip substantially oriented inthe cross-machine direction, thereby defining a cross-machine directionperforate nip between the cross-machine direction elements for embossingand perforating the web, and wherein the cross-machine directionelements have sidewall angles, the angle between the sidewall and theradial direction on the cross-machine direction sides of the element,juxtaposed so as to be capable of producing a shear line, of less thanabout 20°. In one embodiment the cross-machine direction elements havecross-machine direction sidewall angles of less than about 17°. Inanother embodiment the cross-machine direction elements havecross-machine direction sidewall angles of less than about 14°. In yetanother embodiment, the cross-machine direction elements havecross-machine direction sidewall angles of less than 11°. In a furtherembodiment the cross-machine direction elements have cross-machinedirection sidewall angles of from about 7° to 11°.

In yet another embodiment, the invention includes a method for embossingand perforating at least a portion of a web comprising providing a firstembossing roll having embossing elements and providing at least a secondembossing roll having embossing elements, wherein at least a predominatenumber of the embossing elements, when juxtaposed such that they arecapable of producing perforate nips, are substantially oriented in thecross-machine direction and wherein the first and second embossing rollsdefine a perforate nip for embossing and perforating the web and passingthe web between the first and second embossing rolls wherein the firstand second embossing rolls are configured to result in an elementclearance that will achieve a non-picking clearance while achieving atleast a 15% reduction in the machine direction tensile strength of theweb. We have found that picking may be alleviated by controlling thecircumferential alignment of the two rolls. Picking can result fromdrift caused by local variances in roll diameter or gearing from theideal.

In still yet another embodiment, the invention includes a method forreducing the tensile ratio of a web by embossing and perforating the webcomprising passing a web through an embossing system, wherein theembossing system comprises a first embossing roll having embossingelements and at least a second embossing roll having embossing elements,wherein the first and second embossing rolls define a plurality ofperforating nips for embossing and perforating the web and wherein atleast a predominant number of the perforating nips which aresubstantially oriented in the cross-machine direction. In oneembodiment, the invention further includes an embossing system whereinsubstantially all of the embossing elements of the first and secondembossing rolls produce perforating nips which are substantiallyoriented in the cross-machine direction. Further, in one embodiment, thecross-machine embossing elements are at an angle of 85-95° from themachine direction.

In yet another embodiment, the invention includes a method for reducingthe tensile ratio of a web by embossing and perforating the webcomprising passing a web through an embossing system, wherein theembossing system comprises a first embossing roll and at least a secondembossing roll, wherein each of the first and second embossing rolls hasat least one juxtaposable embossing element capable of producing aperforating nip substantially oriented in the cross-machine direction,thereby defining a cross-machine direction perforate nip between thecross-machine direction elements for embossing and perforating the weband wherein at least a substantial portion of the cross-machinedirection elements have at least the ends beveled.

In still yet another embodiment, the invention includes a method forreducing the tensile ratio of a web by embossing and perforating the webcomprising, passing a web through an embossing system, wherein theembossing system comprises a first embossing roll and at least a secondembossing roll, wherein each of the first and second embossing rolls hasat least one juxtaposable embossing element capable of producing aperforating nip substantially oriented in the cross-machine direction,thereby defining a cross-machine direction perforate nip between thecross-machine direction elements for embossing and perforating the weband wherein the cross-machine direction elements have cross-machinedirection sidewall angles of less than about 200. In one embodiment thecross-machine direction elements have cross-machine direction sidewallangles of less than about 17°. In another embodiment the cross-machinedirection elements have cross-machine direction sidewall angles of lessthan about 14°. In yet another embodiment, the cross-machine directionelements have cross-machine direction sidewall angles of less than about11°. In still yet another embodiment, the cross-machine directionelements have cross-machine direction sidewall angles of from about 7°to 11°.

In another embodiment, the invention includes a method for reducing thetensile ratio of a web by embossing and perforating the web comprisingpassing a web through an embossing system, wherein the embossing systemcomprises a first embossing roll having embossing elements and at leasta second embossing roll having embossing elements, wherein the first andsecond embossing rolls define a perforate nip for embossing andperforating the web and wherein the first and second embossing rolls areconfigured to result in an element clearance that will achieve anon-picking clearance.

The invention further includes a perforate embossed web having aplurality of cross-machine direction oriented perforations wherein theembossed web has a tensile ratio of less than about 1.2. The inventionfurther includes a perforate embossed web having a transluminance ratio(as defined hereinafter) of at least 1.005. Still further, the inventionincludes a wet-laid cellulosic perforate embossed web having perforateembossments extending predominately in the cross-machine direction.

The invention still further includes a method of embossing andperforating the web comprising passing a web through an embossingsystem, wherein the embossing system comprises a first embossing rollhaving embossing elements and at least a second embossing roll havingembossing elements, wherein the first and second embossing rolls definea plurality of perforate nips for embossing and perforating the web, andwherein the tensile ratio of the web is reduced.

The invention further includes an embossing system for perforateembossing at least a portion of a web comprising a first embossing rollhaving embossing elements, and at least a second embossing roll havingembossing elements, wherein at least a portion of either the first orsecond embossing rolls is crowned, and wherein the embossing elements ofthe first and second embossing rolls define perforate nips for embossingand perforating the web, and wherein at least a portion of the perforatenips are substantially oriented in the cross-machine direction. Theinvention still further includes an embossing system for embossing andperforating at least a portion of a web comprising a first embossingroll having embossing elements, wherein at least a portion of the firstembossing roll is crowned, and at least a second embossing roll havingembossing elements, wherein the embossing elements of the first andsecond embossing rolls define perforate nips for embossing andperforating the web, and wherein at least a portion of the perforatenips are substantially oriented in the cross-machine direction.

In another embodiment, the invention includes an embossing roll havingembossing elements substantially oriented in the cross-machine directionwherein the embossing roll is crowned.

In yet another embodiment, the invention includes an embossing systemfor embossing and perforating at least a portion of a web comprising afirst embossing roll having embossing elements, the first embossing rollbeing in communication with a first gear, and at least a secondembossing roll having embossing elements, the second embossing rollbeing in communication with a second gear, wherein the embossingelements of the first and second embossing rolls define perforate nipsfor embossing and perforating the web, and wherein at least a portion ofthe perforate nips are substantially oriented in the cross-machinedirection, and wherein the first gear and the second gear have aprecision rating of greater than Q-6. The first gear and the second gearmay have a precision rating of at least about Q-8.

Finally, the invention includes an embossing system for embossing andperforating at least a portion of a web comprising a first embossingroll having embossing elements and at least a second embossing rollhaving embossing elements, wherein the embossing rolls have an alignmentmeans. In one embodiment the first embossing roll has a first alignmentmeans and the second embossing roll has a second alignment means,wherein the embossing elements of the first and second embossing rollsdefine perforate nips for embossing and perforating the web.

The accompanying drawings, which are incorporated herein and constitutea part of this specification, illustrate an embodiment of the invention,and, together with the description, serve to explain the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-D illustrates embossing rolls having cross-machine directionelements according to an embodiment of the present invention.

FIG. 2 illustrates cross-machine direction elements according to anotherembodiment of the present invention.

FIG. 3 illustrates cross-machine direction elements according to anotherembodiment of the present invention.

FIG. 4 illustrates the alignment of the cross-machine direction elementsaccording to an embodiment of the present invention.

FIG. 5 illustrates the alignment of the cross-machine direction elementsaccording to another embodiment of the present invention.

FIG. 6 illustrates the alignment of the cross-machine direction elementsaccording to another embodiment of the present invention.

FIG. 7 illustrates the alignment of the cross-machine direction elementsaccording to yet another embodiment of the present invention.

FIG. 8 is a photomicrograph illustrating the effect of cross-machinedirection elements on a web according to an embodiment of the presentinvention.

FIG. 9 is a photomicrograph illustrating the effect of cross-machinedirection elements on a web according to another embodiment of thepresent invention.

FIG. 10 illustrates the effect of cross-machine direction elements on aweb according to yet another embodiment of the present invention.

FIG. 11 illustrates the effect of cross-machine direction elements on aweb according to yet another embodiment of the present invention.

FIGS. 12A-C are side views of the cross-machine direction elements ofembodiments of the present invention having differing wall angles andillustrating the effect of the differing wall angles.

FIGS. 13A-C are side views of the cross-machine direction elements ofembodiments of the present invention having differing wall angles andillustrating the effect of the differing wall angles.

FIGS. 14A-C are side views of the cross-machine direction elements ofyet another embodiment of the present invention having differing wallangles and illustrating the effect of the differing wall angles.

FIG. 15 depicts a transluminance test apparatus.

FIGS. 16A-B illustrate embossing rolls having both cross-machinedirection and machine direction elements according to an embodiment ofthe present invention.

FIGS. 17A-C illustrate the effects of over embossing a web portion inthe machine direction and cross-machine direction when using rigid toresilient embossing as compared to perforate embossing a web as in FIG.17D.

FIG. 18 depicts a sectional view of a gear and hub assembly of anembossing roll system usable in an embodiment of the present invention.

FIG. 19 depicts a sectional view of a hub assembly usable in anembodiment of the present invention.

FIGS. 20-23 are photomicrographs illustrating the effect of elementdrift according to an embodiment of the present invention.

FIG. 24 illustrates an alignment ring usable in an embodiment of thepresent invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

The present invention can be used to emboss a variety of types ofwet-laid cellulosic webs including paper, and the like. The webs can becontinuous or of a fixed length. Moreover, embossed webs can be used toproduce any art recognized product, including, but not limited to, papertowels, napkins, tissue, or the like. Moreover, the resulting productcan be a single ply or a multi-ply paper product, or a laminated paperproduct having multiple plies. In addition, the present invention can beused with a web made from virgin furnish, recycled furnish, or a webcontaining both virgin and recycled furnish, synthetic fibers, or anycombination thereof.

In accordance with the invention, as broadly described, the convertingprocess includes an embossing system of at least two embossing rolls,the embossing rolls defining at least one nip through which a web to beembossed is passed. The embossing elements are patterned to createperforations in the web as it is passed through the nip.

Generally, for purposes of this invention, perforations are created whenthe strength of the web is locally degraded between two bypassingembossing elements resulting in either (1) a macro scalethrough-aperture or (2) in those cases where a macro scalethrough-aperture is not present, at least incipient tearing, where suchtearing would increase the transmittivity of light through a smallregion of the web or would decrease the machine direction strength of aweb by at least 15% for a given range of embossing depths. Graph 1depicts a comparison of the effects on reduction of strength in themachine direction when perforate embossing a web, as defined herein, andnon-perforate embossing a web. In particular, a conventional wet pressedbase sheet was perforate embossed between two steel rolls. The same basesheet was non-perforate embossed in a rubber to steel configuration. Inaddition, a through-air-dried base sheet was also perforate andnon-perforate embossed. The reduction in machine direction strength wasmeasured for each of the sheets. The results are plotted on Graph 1.

As shown in Graph 1, when non-perforate embossing either a CWP or TADweb to depths of up to 40 mils, the reduction of paper strength in themachine direction is less than 5%. And, when non-perforate embossingeither of the CWP or TAD webs at a depth of 80 mils, the reduction ofstrength of the web is less than 15%. When perforate embossing a web asdisclosed in this invention, a greater reduction in strength of the webcan be achieved. In the example set forth herein, strength reductions ofgreater than 15% are achieved when perforate embossing at depths of atleast about 15 mils as compared to rubber to steel embossing which canresult in these strength losses at emboss depths of over 60 mils.Accordingly, for purposes of this invention, perforation is specificallydefined as locally degrading the strength of the web between twobypassing embossing elements resulting in either (1) the formation of amacro scale through-aperture or (2) when a macro scale through-apertureis not formed, at least incipient tearing, where such tearing wouldeither increase the transmittivity of light through a small region ofthe web or would decrease the machine direction strength of a web by atleast the percentages set forth in Graph 1, wherein the “at least”percentages are indicated by the dashed line.

Not being bound by theory, we believe that the superior strengthreduction results achieved using the present invention are due to thelocation of the local degradation of the web when perforate embossing ascompared to when non-perforate embossing. When a web is embossed, eitherby perforate or non-perforate methods, the portion of the web subject tothe perforate or non-perforate nip is degraded. In particular, as a webpasses through a non-perforate nip for embossing, the web is stressedbetween the two embossing surfaces such that the fiber bonds arestretched and sometimes, when the web is over embossed, which is notdesired when non-perforate embossing a web, the bonds are torn orbroken. When a web is passed through a perforate nip, the web fiberbonds are at least incipiently torn by the stresses caused by the twobypassing perforate elements. As stated above, however, one differencebetween the two methods appears to be in the location of the at leastincipient tearing.

When a web is over-embossed in a rubber to steel configuration, the malesteel embossing elements apply pressure to the web and the rubber roll,causing the rubber to deflect away from the pressure, while the rubberalso pushes back. As the male embossing elements roll across the rubberroll during the embossing process, the male elements press the web intothe rubber roll which causes tension in the web at the area of the weblocated at the top edges of the deflected rubber roll, i.e., at theareas at the base of the male embossing elements. When the web isover-embossed, tearing can occur at these high-tension areas. Moreparticularly, FIGS. 17A-C depict rubber to steel embossing of a web atvarious embossing depths. FIG. 17A depicts embossing of a web atapproximately 0 mils. In this configuration the rubber roll pins the webat the points where the web contacts the steel roll element tops.Typically no tearing will occur in this configuration. In FIG. 17B,where the embossing depth is approximately the height of the steelembossing element, the web is pinned at the element tops and at a pointbetween the bases of the adjacent steel elements. As with theconfiguration depicted in FIG. 17A, tearing does not typically occur inthis configuration for conventional embossing procedures. FIG. 17Cdepicts an embossing depth comparable to or greater than the height ofthe steel element. In this configuration, the “free span” of the web,i.e., the sections of the web that are not pinned between the rubber andsteel rolls, becomes shorter as the rubber material fills the areabetween the adjacent elements. When web rupturing occurs, it tends tooccur near the last location where web movement is possible; that is,the area of degradation 40 is the last area that is filled by the rubbermaterial, namely the corners where the bases of the elements meet thesurface of the emboss roll.

When a web is perforate embossed, on the other hand, the areas ofdegradation 42, as shown in FIG. 17D, are located along the sides of theperforate embossing element. For clarity, only one pair of cooperatingelements are being shown in FIG. 17D. It appears that as a result ofthis difference the degradation of the web and the resultant reductionof web strength is dramatically different.

In one embodiment according to the present invention, the embossingrolls have substantially identical embossing element patterns, with atleast a portion of the embossing elements configured such that they arecapable of producing perforating nips which are capable of perforatingthe web. As the web is passed through the nip, an embossing pattern isimparted on the web. It is preferred that the embossing rolls be eithersteel or hard rubber, or other suitable polymer. The direction of theweb as it passes through the nip is referred to as the machinedirection. The transverse direction of the web that spans the embossroll is referred to as the cross-machine direction. In one embodiment, apredominant number, i.e., at least 50% or more, of the perforations areconfigured to be oriented such that the major axis of the perforation issubstantially oriented in the cross-machine direction. An embossingelement is substantially oriented in the cross-machine direction whenthe long axis of the perforation nip formed by the embossing element isat an angle of from about 60° to 120° from the machine direction of theweb.

In an embodiment according to the present invention, and as shown inFIG. 1, the converting process includes an embossing system 20 of twoembossing rolls 22 defining a nip 28 through which the web 32 to beembossed is passed. According to one embodiment, the embossing rolls 22are matched (i.e., substantially similar, or at least close to,identical male) embossing rolls. The embossing rolls can be, forexample, either steel or hard rubber, or other suitable polymer. Theembossing rolls 22 are configured such that the perforations created bythe embossing elements 34 are oriented such that the major axis of theperforations extend in the cross-machine direction, i.e., the elementsare in the cross-machine direction, although it is possible to envisageconfigurations in which perforations extending in the cross-machinedirection are formed by elements which are longer in the machinedirection, although such a configuration would normally be sub-optimalas it would compromise the overall number of perforations which could beformed in the web. Accordingly, when we discuss elements oriented in thecross-machine direction, we are referring to elements that areconfigured such that the orientation of the perforation formed by thoseelements extends in the cross-machine direction, irrespective of theshape of the remainder of the element not contributing to the shape ofthe nip. While the embossing rolls 22 can also have embossing elementsoriented such that the major axis of the elements is in the machinedirection, a predominant number, i.e., at least 50% or more, of theelements 34 should be oriented such that they are capable of producingperforating nips extending in the cross-machine direction. In anotherembodiment, substantially all, i.e., at least more than 75%, of theelements 34 are oriented such that they are capable of producingperforating nips extending in the cross-machine direction. In yetanother embodiment, all of the elements are oriented in thecross-machine direction. Moreover, at least about 25% of thecross-machine direction elements are perforating elements. In oneembodiment, all of the cross-machine direction elements are perforatingelements. Thus, when the web passes through the embossing rolls 22, atleast a portion of the cross-machine direction elements are aligned suchthat the web is perforated such that at least a portion of theperforations are substantially oriented in the cross-machine direction.

The end product characteristics of a cross-machine direction perforatedembossed product can depend upon a variety of factors of the embossingelements that are imparting a pattern on the web. These factors caninclude one or more of the following: embossing element height, angle,shape, including sidewall angle, spacing, engagement, and alignment, aswell as the physical properties of the rolls, base sheet, and otherfactors. Following is a discussion of a number of these factors.

An individual embossing element 34 has certain physical properties, suchas height, angle, and shape, that affect the embossing pattern during anembossing process. The embossing element can be either a male embossingelement or a female embossing element. The height of an element is thedistance the element 34 protrudes from the surface of the embossing roll22. It is preferred that the embossing elements 34 have a height of atleast about 15 mils. In one embodiment according to the presentinvention, the cross-machine direction elements 34 have a height of atleast about 30 mils. In another embodiment of the present invention, thecross-machine direction elements 34 have a height of greater than about45 mils. In yet another embodiment of the invention, the cross-machineelements have a height of greater than about 60 mils. In yet anotherembodiment, a plurality of the elements 34 on the roll have at least tworegions having a first region having elements having a first height andat least a second region having elements having a second height. In oneembodiment, the elements 34 have a height of between about 30 to 65mils. Those of ordinary skill in the art will understand that there area variety of element heights that can be used, depending upon a varietyof factors, such as the type of web being embossed and the desired endproduct.

The angle of the cross-machine direction elements 34 substantiallydefines the direction of the degradation of the web due to cross-machineperforate embossing. When the elements 34 are oriented at an angle ofabout 90° from the machine direction, i.e., in the absolutecross-machine direction, the perforation of the web can be substantiallyin the direction of about 90° from the machine direction and, thus, thedegradation of web strength is substantially in the machine direction.On the other hand, when the elements 34 are oriented at an angle fromthe absolute cross-machine direction, degradation of strength in themachine direction will be less and degradation of strength in thecross-machine direction will be more as compared to a system where theelements 34 are in the absolute cross-machine direction.

The angle of the elements 34 can be selected based on the desiredproperties of the end product. Thus, the selected angle can be any anglethat results in the desired end product. In an embodiment according tothe present invention, the cross-machine direction elements 34 can beoriented at an angle of at least about 60° from the machine direction ofthe web and less than about 120° from the machine direction of the web.In another embodiment, the cross-machine direction elements 34 areoriented at an angle from at least about 75° from the machine directionof the web and less than about 105° from the machine direction of theweb. In yet another embodiment, the cross-machine direction elements 34are oriented at an angle from at least about 80° from the . . . machinedirection of the web and less than about 100° from the machine directionof the web. In a preferred embodiment, the cross-machine directionelements 34 are oriented at an angle of about 85-95° from the machinedirection.

A variety of element shapes can be successfully used in the presentinvention. The element shape is the “footprint” of the top surface ofthe element, as well as the side profile of the element. It is preferredthat the elements 34 have a length (in the cross-machinedirection)/width (in the machine direction) (L/W) aspect ratio of atleast greater than 1.0, however while noted above as sub-optimal, theelements 34 can have an aspect ratio of less than 1.0.

It is further preferred that the aspect ratio be about 2.0. One elementshape that can be used in this invention is a hexagonal element, asdepicted in FIG. 2. Another element shape, termed an oval, is depictedin FIG. 3. For oval elements, it is preferred that the ends have radiiof at least about 0.003″ and less than about 0.030″ for at least theside of the element forming a perforate nip. In one embodiment, the endradii are about 0.0135″. Those of ordinary skill in the art willunderstand that a variety of different embossing element shapes, such asrectangular, can be employed to vary the embossing pattern.

In one embodiment, at least a portion of the elements 34 are beveled. Inparticular, in one embodiment the ends of a portion of the elements 34are beveled. Oval elements with beveled edges are depicted in FIG. 1. Bybeveling the edges, the disruptions caused by the embossing elements canbe better directed in the cross-machine direction, thereby reducingcross-machine direction degradation caused by the unintentional machinedirection disruptions. The bevel dimensions can be from at least about0.010″ to at least about 0.025″ long in the cross-machine direction andfrom at least about 0.005″ to at least about 0.015″ in the z-direction.Other elements, such as hexagonal elements, can be beveled, as well.

The cross-machine direction sidewall of the elements 34 defines thecutting edge of the elements 34. According to one embodiment of thepresent invention, the cross-machine direction sidewalls of the elements34 are angled. As such, when the cross-machine direction sidewalls areangled, the base of the element 34 has a width that is larger than thatof the top of the element. In one embodiment, the cross-machinedirection sidewall angle be less than about 20°. In another embodiment,the cross-machine direction sidewall angle be less than about 17°. Inyet another embodiment, the cross-machine direction sidewall angle beless than about 14°. Finally, in still yet another embodiment, thecross-machine direction sidewall angle is less than about 11°. It isfurther preferred that the cross-machine direction sidewall angle bebetween about 7° and 11°.

When the opposing elements 34 of the embossing rolls are engaged witheach other during an embossing process, the effect on the web isimpacted by at least element spacing, engagement, and alignment. Whenperforate embossing, the elements 34 are spaced such that the clearancebetween the sidewalls of elements of a pair, i.e., one element 34 fromeach of the opposing embossing rolls 22, creates a nip that perforatesthe web as it is passed though the embossing rolls 22. If the clearancebetween elements 34 on opposing rolls is too great, the desiredperforation of the web may not occur. On the other hand, if theclearance between elements 34 is too little, the physical properties ofthe finished product may be degraded excessively or the embossingelements themselves could be damaged. The required level of engagementof the embossing rolls is at least a function of the embossing pattern(element array, sidewall angle, and element height), and the base sheetproperties, e.g., basis weight, caliper, strength, and stretch. At aminimum, it is preferred that the clearances between the sidewalls ofthe opposing elements of the element pair be sufficient to avoidinterference between the elements. In one embodiment, the minimumclearance is about a large fraction of the thickness of the base sheet.For example, if a conventional wet press (CWP) base sheet having athickness of 4 mils is being embossed, the clearance can be at leastabout 2-3 mils. If the base sheet is formed by a process which resultsin a web with rather more bulk, such as, for example, a through airdried. (TAD) method or by use of an undulatory creping blade, theclearance could desirably be relatively less. Those of ordinary skill inthe art will be able to determine the desired element spacing of thepresent invention based on the factors discussed above using theprinciples and examples discussed further herein.

As noted above, in one embodiment it is preferred that the height of theelements 34 be at least about 30 mils, and it is further preferred thatthe height be from about 30 to 65 mils. Engagement, as used herein, isthe overlap in the z-direction of the elements from opposing embossingrolls when they are engaged to form a perforating nip. The engagementoverlap should be at least 1 mil.

In one embodiment, the engagement is at least about 15 mils. Variousengagements are depicted in FIGS. 12-14. In particular, FIG. 12 depictsa 32 mil engagement. That is, the overlap of the elements, in thez-direction, is 32 mils. The desired engagement is determined by avariety of factors, including element height, element sidewall angle,element spacing, desired effect of the embossing elements on the basesheet, and the base sheet properties, e.g., basis weight, caliper,strength, and stretch. Those of ordinary skill in the art willunderstand that a variety of engagements can be employed based on theabove, as well as other factors. It is preferred that the engagement bechosen to substantially degrade the machine direction tensile strengthof the web. It is further preferred that the engagement be at leastabout 5 mils.

In one embodiment, where the element height is about 42.5 mils and theelements have sidewall angles of from about 7° to 11°, the engagementrange can be from about 16 to 32 mils. FIG. 12 depicts a 32 milengagement, where the element heights are 42.5 mils and the sidewallangles are 7°, 9°, and 11°. It is believed that lower sidewall anglesmake the process significantly easier to run with more controllabilityand decreased tendency to “picking.”

The element alignment also affects the degradation of the web in themachine and cross-machine directions. Element alignment refers to thealignment in the cross-machine direction within the embossing elementpairs when the embossing rolls are engaged. FIG. 4 depicts an embodimentincluding hexagonal embossing elements having a full step alignment,i.e., where the elements are completely overlapped in the cross-machinedirection. FIG. 5. depicts an embodiment wherein hexagonal embossingelements are in half step alignment, i.e., where the elements of eachelement pair are staggered so that half of the engaged portion of theircross-machine direction dimensions overlap. FIG. 6. depicts anembodiment wherein hexagonal embossing elements are in quarter stepalignment, i.e., where the elements of each element pair are staggeredso that one quarter of the engaged portion of their cross-machinedirection dimensions overlap. The embodiment depicted in FIG. 7 is astaggered array, wherein each element pair is in half step alignmentwith adjacent element pairs. Those of ordinary skill in the art willunderstand that a variety of element alignments are available for usewith this invention, depending upon preferred embossing patterns, webstrength requirements, and other factors.

FIGS. 8-9 depict the effects of various alignments of a hexagonalelement arrangement on a web. In the example depicted in FIG. 8, wherethe elements are in full step alignment, perforations exist only in thecross-machine direction in the area between the element pairs. However,between the pairs of element pairs, occasional machine directionperforations can be caused in the machine direction. The result is adegradation of strength in both the machine and cross-machinedirections. In the example depicted in FIG. 9, the web is embossed byelement pairs in half step alignment. In this example, the pperforations exist primarily in the cross-machine direction, with someminor perforations caused in the machine-direction. Thus, in FIG. 9,machine direction strength is degraded, and cross-machine directionstrength is degraded to a lesser extent.

As noted above, the elements can be both in the machine direction andcross-machine direction. FIG. 16 depicts an emboss roll havingcross-machine direction and machine direction hexagonal elements.

In another embodiment, depicted in FIG. 10, beveled oval elements are infull step alignment. As with the full step hexagonal elements discussedabove, in the area between the element pairs perforations existprimarily in the cross-machine direction. However, between the pairs ofelement pairs, perforations can be caused in the machine direction. Theresult is a degradation of strength in both the machine andcross-machine directions. In the embodiment depicted in FIG. 11, on theother hand, where the beveled oval elements in a half step alignment areemployed, the machine direction perforations are substantially reduced.In particular, between the elements in half step alignment, theperforation lies primarily in the cross-machine direction. Between theelement pairs, which are in zero step alignment, primarily pinpointruptures exist. These pinpoint ruptures have a minor effect ondegradation of the directional properties of the web.

Those of ordinary skill in the art will understand that numerousdifferent configurations of the above described element parameters,i.e., element shape, angle, sidewall angle, spacing, height, engagement,and alignment, can be employed in the present invention. The selectionof each of these parameters may depend upon the base sheet used, thedesired end product, or a variety of other factors.

One factor, which is impacted by these parameters, is “picking” of theweb as it is embossed. Picking is the occurrence of fiber being left onthe embossing roll or rolls as the web is embossed. Fiber on the rollcan diminish the runability of the process for embossing the web,thereby interfering with embossing performance. When the performance ofthe embossing rolls is diminished to the point that the end product isnot acceptable or the rolls are being damaged, it is necessary to stopthe embossing process so that the embossing rolls can be cleaned. Withany embossing process, there is normally a small amount of fiber left onthe roll which does not interfere with the process if the roll isinspected periodically, e.g., weekly, and cleaned, if necessary. Forpurposes of the invention, we define picking as the deposition of fiberon the rolls at a rate that would require shut down for cleaning of therolls more frequently than once a week.

EXAMPLES

The following examples exhibit the occurrence of picking observed incertain arrangements of cross-machine direction perforate embossedpatterns. This data was generated during trials using steel embossingrolls engraved with the cross-machine direction beveled oval embossingpattern at three different sidewall angles. In particular, the embossingrolls were engraved with three separate regions on the rolls—a 7°embossing pattern, a 9° embossing pattern, and an 11° embossing pattern.Two trials were performed. In the first trial, the embossing rolls hadan element height of 45 mils. The base sheet, having a thickness of 6.4mils, was embossed at engagements of 16, 24, and 32 mils. In the secondtrial, the steel rolls were modified by grinding 2.5 mils off the topsof the embossing elements, thereby reducing the element height to 42.5mils and increasing the surface area of the element tops. The base sheethaving a thickness of 6.2 mils was embossed at engagements of 16, 24,28, and 32 mils. For each trial, embossing was performed in both halfstep and full step alignment.

The element clearances for each of the sidewall angles of the first andsecond trials have been plotted against embossing engagement in Graphs 2and 3, respectively. The broken horizontal line on each plot indicatesthe caliper of a single ply of the base sheet that was embossed. Thegraphs have been annotated to show whether fiber picking was observed ateach of the trial conditions (half step observation being to the left ofthe slash, full step observation to the right). The picking results aredepicted in Graphs 2 and 3 below.

Graph 2 shows that for this particular trial using embossing rollshaving a 45 mil element height, picking did not occur at any of thesidewall angles. However, as shown in Graph 3, when the embossing rollshaving a 42.5 mil element height were run, fiber picking was observed onthe 11° sidewall angle elements at the higher embossing engagements,i.e., 24, 28, and 32 mils. No fiber picking was encountered withelements having sidewall angles of 7° or 9°.

Based on the observed data, it appears that picking is a function of theelement height, engagement, spacing, clearance, sidewall angle,alignment, and the particular physical properties of the base sheet,including base sheet caliper. An example of element clearance can beseen in FIG. 12, where the side profiles of the 42.5 mil elements(having 7°, 9°, and 11° sidewall angles) at 32 mil embossing engagementare shown. Clearance is the distance between adjacent engaging embossingelements. As noted above, the caliper of the embossed sheet for thistrial was 6.2 mils. As shown in FIG. 12, the calculated or theoreticalclearance at 7° is 0.004906″. (4.906 mils), the clearance at 90 is0.003911″ (3.911 mils), and the clearance at 11° is 0.00311″ (3.11mils). Thus, for this trial at a 32 mil engagement, picking was observedonly when the clearance was less than about ½ of the caliper of thesheet. Compare this to the clearances shown in FIG. 13. FIG. 13 depictsthe sidewall profiles of the 42.5 mil elements at 28 mil embossingengagement. In this arrangement, the calculated or theoretical clearanceat 7° is 0.006535″ (6.535 mils), the clearance at 9° is 0.005540″ (5.540mils), and the clearance at 110 is 0.004745″ (4.745 mils). In thistrial, picking was observed when the clearance was less than about ¾ ofthe caliper of the sheet. Note, however, that when embossing at 32 mils,as described above, picking did not occur at 9°, while the clearance wasless than 4.745 mils. FIG. 14 depicts the sidewall profiles of the 42.5mil elements at 24 mil engagement. In this arrangement, the clearance at11° is 0.005599″ (5.599 mils), slightly less than the caliper of thesheet. As shown on Graph 3, picking did occur for these elements, butonly when the elements were in full step alignment and not when in halfstep alignment. And, as shown in Graph 2, picking did not occur at all,at any angle, engagement, or alignment, for the 45 mil embossing rolls.

Thus, based on the collected data, picking can be controlled by varyingelement height, engagement, spacing, clearance, alignment, sidewallangle, roll condition, and the physical properties of the base sheet.Based upon the exemplified information, those of ordinary skill in theart will understand the effects of the various parameters and will beable to determine the various arrangements that will at least achieve anon-picking operation, i.e., the configuration required to avoid anunacceptable amount of picking based on the factors discussed above,and, hence, produce acceptable paper products with a process that doesnot require excessive downtime for roll cleaning.

To establish the effectiveness of the various element patterns inperforating the web in the cross-machine direction, and therebydegrading machine direction strength while maintaining cross-machinedirection strength, a test was developed, the transluminance test, toquantify a characteristic of perforated embossed webs that is readilyobserved with the human eye. A perforated embossed web that ispositioned over a light source will exhibit pinpoints of light intransmission when viewed at a low angle and from certain directions. Thedirection from which the sample must be viewed, e.g., machine directionor cross-machine direction, in order to see the light, is dependent uponthe orientation of the embossing elements. Machine direction orientedembossing elements tend to generate machine direction ruptures in theweb which can be primarily seen when viewing the web in thecross-machine direction. Cross-machine direction oriented embossingelements, on the other hand, tend to generate cross-machine directionruptures in the web which can be seen primarily when viewing the web inthe machine direction.

The transluminance test apparatus, as depicted in FIG. 15, consists of apiece of cylindrical tube 44 that is approximately 8.5∝ long and cut ata 28° angle. The inside surface of the tube is painted flat black tominimize the reflection noise in the readings. Light transmitted throughthe web itself, and not through a rupture, is an example of a non-targetlight source that could contribute to translucency noise which couldlead non-perforate embossed webs to have transluminance ratios slightlyexceeding 1.0, but typically by no more than about 0.05 points. Adetector 46, attached to the non-angled end of the pipe, measures thetransluminance of the sample. A light table 48, having a translucentglass surface, is the light source.

The test is performed by placing the sample 50 in the desiredorientation on the light table 48. The detector 46 is placed on top ofthe sample 50 with the long axis of the tube 44 aligned with the axis ofthe sample 50, either the machine direction or cross-machine direction,that is being measured and the reading on a digital illuminometer 52 isrecorded. The sample 50 is turned 90° and the procedure is repeated.This is done two more times until all four views, two in the machinedirection and two in the cross-machine direction, are measured. In orderto reduce variability, all, four measurements are taken on the same areaof the sample 50 and the sample 50 is always placed in the same locationon the light table 48. To evaluate the transluminance ratio, the twomachine direction readings are summed and divided by the sum of the twocross-machine direction readings.

To illustrate the results achieved when perforate embossing withcross-machine direction elements as compared to machine directionelements, a variety of webs were tested according to the above describedtransluminance test. The results of the test are shown in Table 1. TABLE1 Transluminance Ratios Basis Trans- Weight Creping Method Emboss Embossluminance (lbs/ream) (Blade) Alignment Pattern Ratio 30 Undulatory FullStep CD Beveled Oval 1.074 30 Undulatory Half Step CD Beveled Oval 1.05632 Undulatory Half Step CD Beveled Oval 1.050 30 Undulatory Half Step CDOval 1.047 31 Undulatory Half Step CD Oval 1.044 31 Undulatory Full StepCD Oval 1.043 30 Undulatory Full Step CD Beveled Oval 1.040 32Undulatory Half Step CD Beveled Oval 1.033 30 Undulatory Half Step CDBeveled Oval 1.033 30 Undulatory Full Step CD Oval 1.027 32 UndulatoryHalf Step CD Beveled Oval 1.025 30 Undulatory Half Step CD Oval 1.022 31Undulatory Full Step CD Oval 1.018 20 Undulatory Half Step CD BeveledOval 1.015 30 Undulatory Half Step CD Beveled Oval 1.012 30 UndulatoryFull Step CD Beveled Oval 1.006 28 Standard Unknown MD Perforated 1.00024 Undulatory Half Step MD Perforated 0.988 22 Standard Unknown MDPerforated 0.980 29 Undulatory Half Step MD Perforated 0.966 29Undulatory Half Step MD Perforated 0.951 31 Undulatory Half Step MDPerforated 0.942 29 Undulatory Half Step MD Perforated 0.925

A transluminance ratio of greater than 1.000 indicates that the majorityof the perforations are in the cross-machine direction. For embossingrolls having cross-machine direction elements, the majority of theperforations are in the cross-machine direction. And, for the machinedirection perforated webs, the majority of the perforations are in themachine direction. Thus, the transluminance ratio can provide a readymethod of indicating the predominant orientation of the perforations ina web.

As noted above, perforated embossing in the cross-machine directionpreserves cross-machine direction tensile strength. Thus, based on thedesired end product, a web perforate embossed with across-machine-direction pattern will exhibit one of the following whencompared to the same base sheet embossed with a machine directionpattern: (a) a higher cross-machine direction tensile strength atequivalent finished product caliper, or (b) a higher caliper atequivalent finished product cross-machine direction tensile strength.

Furthermore, the tensile ratio (a comparison of the machine directiontensile strength to the cross-machine direction tensile strength—MDstrength/CD strength) of the cross-machine perforate embossed webtypically will be at or below the tensile ratio of the base sheet, whilethe tensile ratio of the sheet embossed using prior art machinedirection perforate embossing typically will be higher than that of thebase sheet. These observations are illustrated by the followingexamples.

Higher cross-machine direction strength at equivalent caliper isdemonstrated in Table 2. This table compares two products perforateembossed from the same base sheet—a 29 pounds per ream (Ibs/R),undulatory blade-creped, conventional wet press (CWP) sheet. TABLE 2Increased CD Strength at Equivalent Caliper MD Dry CD Dry Dry TensileEmboss Basis Wt. Caliper Tensile Tensile Ratio (perforate) (lbs/R)(mils) (g/3″) (g/3″) (MD/CD) CD 29.1 144 3511 3039 1.16 Hexagonal MD29.2 140 4362 1688 2.58 Hexagonal

As shown in Table 2, the cross-machine direction perforate embossed webhas approximately the same caliper as the machine direction perforateembossed web (144 vs. 140 mils, respectively), but its cross-machinedirection dry tensile strength (3039 g/3′) is considerably higher thanthat of the machine direction hexagonal-embossed web (1688 g/3″). Inaddition, compared to the tensile ratio of the base sheet (1.32), thecross-machine direction perforate embossed web has a lower ratio (1.16),while the machine direction perforate embossed web has a higher ratio(2.58). Thus the method of the present invention provides a convenient,low cost way of “squaring” the sheet—that is, bringing the tensile ratiocloser to 1.0.

Higher caliper at equivalent finished product cross-machine directiontensile strength is illustrated by three examples presented in Table 3.For each example a common base sheet (identified above each data set)was perforate embossed with a cross-machine direction and a machinedirection oriented pattern (Hollow Diamond is a machine directionoriented perforate emboss). TABLE 3 Increased Caliper at Equivalent CDTensile Strength MD Dry CD Dry Emboss Basis Wt. Caliper Tensile TensileDry Tensile Ratio (perforate) (lbs/R) (mils) (g/3″) (g/3″) (MD/CD) BaseSheet-undulatory blade-creped, CWP base sheet with tensile ratio = 1.32CD Quilt 28.8 108 4773 4068 1.17 MD Quilt 28.8 78 6448 3880 1.66 BaseSheet-undulatory blade-creped, CWP base sheet with tensile ratio = 1.32CD Quilt 29.5 154 2902 2363 1.23 MD Quilt 29.5 120 5361 2410 2.22 BaseSheet-undulatory blade-creped, CWP base sheet with tensile ratio = 1.94CD Oval 24.6 75 4805 2551 1.88 Hollow 24.1 56 5365 2364 2.27 Diamond

In each case, the cross-machine direction perforate embossed productdisplays enhanced caliper at equivalent cross-machine direction drytensile strength relative to its machine direction perforate embossedcounterpart. Also, the cross-machine direction perforate embossedproduct has a lower tensile ratio, while the machine direction perforateembossed product a higher tensile ratio, when compared to thecorresponding base sheet.

The current invention further allows for a substantial reduction in basepaper weight while maintaining the end product performance of a higherbasis weight product. As shown below in Table 4, wherein the web isformed of recycled fibers, the lower basis weight cross-machinedirection perforate embossed towels achieved similar results to machinedirection perforate embossed toweling made with higher basis weights.TABLE 4 Performance Comparisons. Hollow Hollow Diamond CD Oval DiamondCD Oval (MD (CD (MD (CD EMBOSS Perforate) Perforate) Perforate)Perforate) BASIS WT 24.1 22.2 31.3 28.9 (LBS/REAM) CALIPER 56 62 76 81DRY MD TENSILE 5365 5057 5751 4144 (g/3″) DRY CD TENSILE 2364 2391 36643254 (g/3″) MD STRETCH (%) 7.6 8.1 8.8 10.1 CD STRETCH (%) 6.3 6.1 5.55.3 WET MD CURED 1236 1418 1409 922 TENSILE (g/3″) WET CD CURED 519 597776 641 TENSILE (g/3″) MacBeth 3100 72.3 72.6 73.3 73.4 BRIGHTNESS (%)SAT CAPACITY (g/m²) 98 102 104 119 SINTECH MODULUS 215 163 232 162 BULKDENSITY 367 405 340 385 WET RESILIENCY 0.735 0.725 0.714 0.674 (RATIO)

In Table 4, two comparisons are shown. In the first comparison, a 24.1lbs/ream machine direction perforated web is compared with a 22.2lbs/ream cross-machine direction perforated web. Despite the basisweight difference of 1.9 lbs/ream, most of the web characteristics ofthe lower basis weight web are comparable to, if not better than, thoseof the higher basis weight web. For example, the caliper and the bulkdensity of the cross-machine direction perforated web are each about 10%higher than those of the machine direction perforated web. The wet anddry tensile strengths of the webs are comparable, while the Sintechmodulus of the cross-machine direction perforated web (i.e., the tensilestiffness of the web, where a lower number is preferred) is considerablyless than that of the machine direction perforated web. In the secondcomparison, similar results are achieved in the sense that comparabletensile ratios and physicals can be obtained with a lower basis weightweb. Paradoxically, consumer data indicates that the 28#29C8 product wasrated equivalent to the 30.5#HD product while the 22#30C6 product was atstatistical parity with the 20204 product, but was possibly slightlyless preferred than the 20204 product.

In one embodiment of the present invention, precision gearing andprecision hubs are used to significantly reduce or eliminatecircumferential alignment drift of the embossing rolls. In particular,in a perforate embossing operation, the opposing perforate embossingelements on the embossing rolls are in close proximity to one another.As the embossing rolls rotate during the perforate embossing process,the embossing rolls may have a tendency to drift circumferentiallyrelative to one another. If the embossing rolls drift circumferentially,it is possible that the cross-machine direction elements will interferewith each other, potentially leading to unwanted degradation of thepaper web and, ultimately, to damage or destruction of the elementsthemselves.

Precision gearing and precision hubs can be used to significantly reduceor eliminate circumferential alignment drift of the embossing rolls. Inone embodiment, a precision gear used in the present invention is formedof pre-heat treated material. In another embodiment, a precision gearused in the present invention is formed by precision grinding the stockmaterial, i.e., a ground gear. In yet another embodiment, shaved gearsare used.

FIG. 18 depicts the end of an embossing roll 22, including a journal 60.The journal 60 is in communication with the embossing roll 22 andtransmits rotational movement from the gearing system to the embossingroll 22. Also shown in FIG. 18 is the gear assembly. The gear assemblyincludes a gear 66, a bushing 64, and a hub 62. The hub 62 and bushing64 are in direct communication. In particular, the bushing 64 ispress-fit into the inner diameter of the hub 62. In addition, the gear66 and hub 62 are also in direct communication. In operation, the gear66 transmits rotational movement to the hub 62 and bushing 64, which inturn transmit rotational movement to the journal 60 and embossing roll22. In the embodiment depicted in FIG. 18 the gear is external to theroll. Those of ordinary skill in the art will understand, however, thatthe gear 66 may be integral with the embossing roll 22.

The precision gearing for the present invention may have at least twoelements. First, the gear may be formed with high machine tolerances.Second, the hub and bushing, in which the journal rests, may be formedwith high tolerances in order to maintain the concentricity of theembossing roll.

As noted above, in standard gearing mechanisms the gears are constructedby first forming the gears out of metal block. To achieve the hardnesslevels required for operating conditions, conventional gears are heattreated after the gear teeth are formed. The heat treating processtypically causes deformation in the gears and, therefore, the gears lackthe necessary precision for certain applications. There are three majortechniques for improving the accuracy of gearing which can be usedsingly or in combination to achieve the requires degree of precision:use of pre-heat treated steel, shaving, and precision grinding. In oneembodiment of the present invention, the gear is formed of a basematerial that has been heat treated, i.e., a pre-heat treated basematerial, thus obviating potential deformations created by heat-treatingafter the teeth are formed. The base material can be carbon steel, iron,or other materials or alloys known to those of ordinary skill in theart, or later discovered, to have sufficient-hardness for the presentapplication. One steel that has been used is 4150 HR STL RND, which hasbeen pre-heat treated to 28-32 Rockwell C. The base material is thenhobbed to form the gear structure. The hobbing process includesmachining away the base material and then, if even higher precision isrequired, shaving or precision grinding of the remaining material can beused to form the precision gear. Precision grinding can also be used toimprove precision in gears that have been heat-treated after hobbing.The pitch line TIR (total indicated runout, as measured according toANSI Y14.5M) on the gear should not exceed 0.001″. Because heat treatingis not required after the gear is formed by the hobbing process whenpre-heat treated steel is used, the gear is not distorted after the gearhas been formed.

In another embodiment of the present invention, the gears are shavedgears. Shaved gears may be formed using the following process. First,the non-pre-heat treated material is hobbed. While the process issimilar to the hobbing process described above, the gear is hobbed to belarger than the desired final dimensions. Next the gear is heat treated.After the heat treatment, the gear is then re-hobbed according to thedesired final dimensions.

In yet another embodiment of the present invention, the gears areprecision ground. Precision in gearing is identified by a grading scale.In particular, the AGMA (American Gear Manufacturers Association) ratesthe precision, or quality, of a gear on a “Q” scale. (See “GearClassification and Inspection Handbook,” ANSI/AGMA 2000-A88 (March1988).) For example, the highest precision can generally be found in aground gear. Ground gears generally have a precision grading of Q-10.Hobbed gears, formed from pre-heat treated material as described above,generally have a precision grading of Q-8. Heat treated gears, on theother hand, generally have a grading of Q-6 or less. The precision gearsof the present invention should have a precision rating of greater thanQ-6. In one embodiment the precision gears have a precision rating of atleast about Q-8. In another embodiment of the present invention, thegears have a precision rating of at least about Q-10. Those of ordinaryskill in the art will be able to select the appropriate precision gearbased on a variety of factors, including precision desired and cost ofgearing.

When using a precision gear, a precision hub assembly may also be used.The hub assembly is depicted in FIG. 19. The hub assembly includes thehub 62 and the bushing 64. According to one embodiment, the hub 62 is inpress-fit communication with the bushing 64. The hub assembly is capableof receiving the embossing roll journal. Moreover, the hub assembly iscapable of transmitting rotational movement to the journal. In oneembodiment, the hub assembly is precision formed. Referring to FIG. 19,the precision hub assembly of the present invention is formed bymachining the hub 62 and the bushing 64 together. In particular, the hub62 is placed on an arbor 68 and the bushing 64 is then press-fit betweenthe hub 62 and the arbor 68. The hub 62 and bushing 64 are then machinedto the appropriate dimensions for the application. In particular, theouter diameter of the hub 62 and bushing 64, and the face of the hub 62and bushing 64 are machined as an assembly. After machining, the hubassembly is removed from the arbor and placed in communication with theembossing roll journal. The precision formed hub assembly is capable ofproviding concentricity for the embossing roll when it is rotating. Ahub may be considered a precision hub when the tolerances are such thatthe effect is a reduction or elimination in the circumferentialalignment drift of the embossing rolls. In particular, tolerance shouldbe between approximately 0.00-and 0.0003″ TIR on the hub assembly outerdiameter. In many cases, it will be advantageous to mount the gears tothe roll using a bolt pattern which allows the hub to be only mountedwhen the hub is at a fixed angular position on the roll. Often this isachieved by using uneven angular spacing of the bolt holes.

The resulting improvement from using precision gearing as compared tostandard gearing is evidenced by a reduction in the circumferentialalignment drift of the embossing rolls when using precision gearing.Circumferential alignment drift in the embossing rolls is evidenced bynon-uniformity of the clearance between adjacent engaged embossingelements. Clearance, according to the present invention, is the distancebetween adjacent engaging embossing elements. Accordingly, when theranges of clearance differences between the elements is significant,embossing roll circumferential alignment drift may be present.

FIGS. 20-23 are photomicrographs showing the clearances between adjacentengaging embossing elements for two different embossing roll sets. Inparticular, FIGS. 20 and 21 are photomicrographs of a web that has beencross-machine direction perforate embossed by embossing rolls havingstandard gearing. FIGS. 20 and 21 show the amount of drift betweenadjacent elements for one revolution of the embossing roll set. FIG. 20depicts the closest clearance between the elements while FIG. 21 depictsthe furthest clearance between the elements. Comparing FIGS. 20 and 21,the difference between the closest and furthest clearance issignificant, thereby reflecting a significant circumferential drift inalignment between the embossing rolls.

FIGS. 22 and 23, on the other hand, are photomicrographs of a web thathas been cross-machine direction perforate embossed by embossing rollsusing pre-heat treated gears. FIGS. 22 and 23 show the amount of driftbetween adjacent elements for one revolution of the embossing roll set.FIG. 22 depicts the closest clearance between the elements while FIG. 23depicts the furthest clearance between the elements. Comparing FIGS. 22and 23, the difference between the closest and furthest clearancesbetween the elements is minor, thereby reflecting a minorcircumferential drift in alignment between the embossing rolls.Accordingly, it is evident that precision gearing reduces thecircumferential alignment drift between the embossing rolls.

Those of ordinary skill in the art will be able to determine theacceptable amount of embossing roll circumferential alignment drift. Inparticular, embossing roll circumferential alignment drift should beminimized to avoid interference between the adjacent engaging elementsand to minimize non-uniformity of the perforate embossed web. Inaddition, those of ordinary skill in the art will understand that thecurrent invention is applicable to other applications, such as perforateembossing operations having elements in both the machine andcross-machine directions.

In another embodiment of the present invention, at least-one of theembossing rolls is crowned. A caliper profile may exist when perforatinga web in the cross-machine direction. In particular, when perforating aweb in the cross-machine direction at operating speeds, in someinstances the caliper of the perforated web near the ends of theembossing rolls may be greater than that at the middle of the roll. Thiscaliper profile indicates that a higher degree of perforation wasaccomplished near the ends of the embossing rolls. In theory, it isbelieved that this profile is a function of the speed of the web as itis perforated.

To test this theory, an experiment was conducted. In the experiment,caliper profiles for a cross-machine direction perforated product werecollected. In particular, a web was embossed at both a low running speedand a speed. The embossing elements were in half-step alignmentreadings, data points 1-7, were taken across the width of each Datapoints 1 and 7 were located at the opposite ends of the direction widthof the web, while points 2-6 were located To determine the magnitude ofa caliper profile, the following ed: Delta_(c)=avg. caliper (1 & 7)−avg.caliper (2-6). The was collected. TABLE 5 TRIAL RUN SPEED (FPM)DELTA_(C) (MILS) 1 454 2.7 1 103 0.7 2 436 8.7 2 98 1.5 3 516 7.6 3 1004.3 4 480 6.2 4 100 −2.0

As indicated above, for each of the trials the caliper profile, i.e.,the difference in caliper between the end portions of the web versus themiddle of the web, was more pronounced when the web was perforated athigh, operational, speeds, In particular, when operating at higher,operational speeds the average Delta_(c) was 6.3. When operating atlower speeds, on the other hand, the average Delta_(c) was 1.1. Intheory, it is believed that the caliper profile exists because theembossing rolls flex when the web is embossed at operational speeds. Itis further believed that the profile exists because, while the ends ofthe rolls are fixed at the bearings, the middle of the roll is free toflex, thus resulting in a caliper profile. That is, the middle of theroll is allowed to flex away from the web and, thus, does not emboss themiddle portion of the web at the same level as the ends of the roll.

When it is desired to reduce the caliper profile, a crowned embossingroll may be used. In one embodiment, only one embossing roll of theembossing roll set is crowned. In another embodiment, both embossingrolls of an embossing roll set are crowned. An embossing roll for useaccording to the present invention may be from about 6 inches to about150 inches in width. The average diameter of the embossing roll for usewith this invention may be from about 2.5 inches to at least about 20inches. Selection of the appropriate diameter and width of the embossingroll would be apparent to the skilled artisan based upon a variety offactors, including the width of the web to be embossed and the specificsof the converting machine being used.

In one embodiment, an embossing roll is provided wherein E the diameterof the center portion is greater than that of the ends. That is, theroll is crowned by reducing the diameter of a portion of the embossingroll. In particular, the diameter of the embossing roll is graduallyreduced when moving from the center portion of the embossing rolltowards the ends of the embossing roll. In one embodiment the reductiontowards the ends of the roll being greater such that the shape of thecrown is generally parabolic. The diameter of the embossing roll may bedecreased at the ends from about 1-8 mils. In one embodiment, using anembossing roll having a 10 inch diameter and a 69 inch width, thediametrical crown at the end of the roll is about −2 mils, i.e., thediameter of the ends of the roll is 2 mils less than that at thegreatest diameter of the roll. In one embodiment, the diametrical crownat the ends of the roll is approximately −2.4. Those of ordinary skillin the art will be able to determine the appropriate diameters of thereduced diameter portions based on a variety of factors, including thedesired physical properties of the finished product, the projected speedof the web, the properties of the base sheet being perforate embossed,and the width and diameter and construction of the emboss rolls. Inaddition, those of ordinary skill in the art will understand that whenonly one embossing roll is crowned, instead of both embossing rolls, itmay be necessary that the crown of the crowned roll be greater.

In one example of the above embodiment, the two opposing embossing rollswere crowned. The first embossing roll was crowned at a maximum of 4.1mils and the second embossing roll crowned at a maximum of 3.8 mils.That is, the maximum diameter reductions in the first and second rollswere 4.1 mils and 3.8 mils, respectively. Tables 6 and 7, below, showthe crown dimensions of each of the rolls. The rolls had an embossedface length of 69″. The reference points were measured in approximately5″ intervals. The reference point distance is the distance from thereference point to the journal end of the roll. At the center point ofthe roll, approximately 35″ from the journal end, the crown is “0” asthat is the largest diameter. The crown, or difference in diameterbetween the center point and the reference point, is shown in negativenumbers to indicate that the diameter at that point is less than thecenter point diameter. As indicated, the diameter of the roll decreasesgradually as the distance from the center point increases. TABLE 6 Roll1 Reference Point Diameter of Embossing (inches) Roll (inches) Crown(mils) 1 10.0251 −4.1 5 10.0262 −3.0 10 10.0273 −1.9 15 10.0276 −1.6 2010.0281 −1.1 25 10.0284 −0.8 30 10.0292 0.0 35 10.0292 0.0 40 10.02920.0 45 10.0290 −0.2 50 10.0281 −1.1 55 10.0277 −1.5 60 10.0274 −1.8 6510.0265 −2.7 68 10.0255 −3.7

TABLE 7 Roll 2 Reference Point Diameter of Embossing (inches) Roll(inches) Crown (mils) 1 10.0253 −3.7 5 10.0263 −2.7 10 10.0272 −1.8 1510.0280 −1.0 20 10.0285 −0.5 25 10.0288 −0.2 30 10.0288 −0.2 35 10.02900.0 40 10.0290 0.0 45 10.0285 −0.5 50 10.0282 −0.8 55 10.0277 −1.3 6010.0271 −1.9 65 10.0262 −2.8 68 10.0252 −3.8

Of note, the above measurements were taken prior to the crowned rollbeing chromed. According to one embodiment, the embossing rolls can beplated with chrome. Chrome plating provides added durability, increasedreleasability of the web, and corrosion resistance to the embossingrolls. Co-pending U.S. patent Application Ser. No. 10/187,608, which isincorporated herein by reference, discusses, inter alia, wear resistantcoating for embossing rolls. After the rolls were chromed, referencepoints 1 and 68 of the first roll measured −3.7 mils and −3.3 mils,respectively, while reference points 1 and 68 of the second rollmeasured −3.5 mils and −3.5 mils, respectively.

To determine the effect of the crowned rolls on the caliper profile ofthe perforate embossed web, a trial was conducted using the crownedrolls. During the trial, paper webs were perforate embossed at anaverage speed of 520 feet per minute (the minimum and maximum speedsbeing 472 and 537 feet per minute, respectively) at both full stepalignment and half step alignment. The caliper profile was measured asdescribed above. The average delta, i.e., caliper difference between theends of the roll compared to the middle portion of the web, was −1.8. Incomparison in a similar trial using non-crowned rolls where the paperwebs were perforate embossed in both full step and half step alignmentat an average speed of 484 feet per minute (the minimum and maximumspeeds being 432 and 555 feet per minute, respectively), the averagedelta was 4.6. Thus, based on the achieved results, crowning the rollshas the effect of reducing the caliper profile of the perforate embossedweb.

Those of ordinary skill in the art will understand that various caliperprofiles can be achieved by changing the crown profile of the embossingrolls. For example, in the previously discussed example, the caliperprofile of the web perforate embossed using non-crowned rolls had apositive profile of 4.6 (i.e., the caliper of the perforated web nearthe ends of the embossing rolls was greater than that at the middle ofthe roll). When the described crowned rolls were used, the caliperprofile of the web was slightly negative at −1.8, indicating that thecaliper of the perforated web near the ends of the embossing rolls wasless than that at the middle of the roll. Thus, one of ordinary skill inthe art would readily appreciate that a caliper profile of approximatelyzero could be attained by crowning the rolls by less than theabove-described rolls. For example, the rolls could be crowned byapproximately 2-3 mils.

Those of ordinary skill in the art will understand that the crowningtechnique is applicable to other applications, but our experiencesuggests that it is particularly useful with patterns having substantialnumbers of perforate embossing elements in the cross-machine direction.

In yet another embodiment of the present invention, an alignment meansis provided for the embossing rolls. In one embodiment, an adjustablecollar ring is provided on the first embossing roll. The secondembossing roll may have an adjustable collar ring, a fixed collar, amachined keyway, or other means for identifying a particular position ofthe second embossing roll. In another embodiment of the presentinvention, scribe marks are provided on each of the first and secondembossing rolls.

In one embodiment an adjustable collar ring is provided on an end ofeach of the matched embossing rolls. FIG. 24 depicts a collar for usewith the present invention. The collar 70 includes a plurality of slots72 capable of receiving fastening means (not shown) for attaching thecollar 70 to an end of the embossing roll. The collar 70 should have atleast two slots 72. Those of ordinary skill in the art will understandthat more than two slots can be included in the collar. The collar 70depicted in FIG. 24 has four slots. The collar 70 further includes akeyway 74. The keyway 74 provides the capability of aligning theembossing roll with a second embossing roll having a keyway 74. Thecollar 70 can be made of various materials, including stainless steel,carbon steel, iron, or other appropriate material known by those ofordinary skill in the art, or later discovered, to be suitable for useas a collar for a roll in a paper making machine.

An alignment process for a first and second embossing roll having firstand second adjustable collar rings will now be discussed. In oneembodiment of an embossing operation having first and second embossingrolls, each embossing roll will have a collar on one common end. Theinitial alignment of the embossing rolls is as follows. First, theoperator brings the rolls into close proximity, without allowing contactbetween the cross-machine embossing elements. A web; such as a nipimpression paper, is then fed through the embossing roll, leaving animprint of the location of the elements on the nip impression paper. Theimprinted web is then analyzed to determine whether the elements willcontact each other when the embossing rolls are brought into closerproximity. Based on the outcome of the imprint, the machine directionalignment of the embossing rolls may be adjusted. After any necessaryadjustment, the rolls are brought into closer proximity and a web isonce again fed through the embossing rolls to determine the location ofthe elements. This process is repeated until the embossing rolls, andhence the embossing elements, are in operating engagement position. Oncethe embossing rolls are in position, the collars are aligned such thatthe keyways face each other. A key (not shown) is then placed in theopposing keyways to fix the alignment of the collars. The fasteningmeans are then tightened, thereby setting the collars in place. In oneembodiment, the adjusted collar is pinned into place to preventadjustment of the collar after the initial setting.

For subsequent alignment of the embossing rolls, for example, after oneor both rolls are removed for maintenance purposes, or thecircumferential alignment of either of the rolls is changed for anyreason, the rolls are brought into close proximity, the embossing rollsare maneuvered such that the keyways of the opposing collars are facingeach other, the key is inserted into the keyways, and then the embossingrolls are brought into engagement. Because the embossing rolls havepreviously been aligned, the embossing rolls can be brought intoengagement without substantial risk of interference of the cross-machineelements. After the embossing rolls are brought into engagement, fineadjustments can then be made. Using the present invention, the requiredtime to align the embossing rolls to 0.000″ engagement after the initialalignment is reduced to approximately one hour or less. The initialalignment of the embossing rolls, described above, can be accomplishedeither at the fabrication facility or while the rolls are on the paperconverting machine. Those of ordinary skill in the art will understandthat keying is applicable to other applications, but we have found thatit is particular useful for this application wherein perforate embossingelements extend in the cross-machine direction.

This invention can be used in a variety of different processes. The websin each of the above-described examples were formed in a conventionalwet press process. However, the invention is equally applicable when thebase web is a through air dried web. In addition, to increase thesmoothness of the resulting product, the web may be calendered. Or, asin one of the examples above, to increase the bulkiness of the product,an undulatory creping blade such as described in U.S. Pat. No.5,690,788, which is herein incorporated by reference, may be used. Thoseof ordinary skill in the art will understand the variety of processes inwhich the above-described invention can be employed.

It is understood that the invention is not confined to the particularconstruction and arrangement of parts and the particular processesdescribed herein but embraces such modified forms thereof as come withinthe scope of the following claims.

1. An embossing system for perforate embossing at least a portion of aweb comprising: a first embossing roll having embossing elements; and atleast a second embossing roll having embossing elements, wherein theembossing elements of the first and second embossing rolls defineperforate nips for embossing and perforating the web, wherein at least aportion of at least the first or second embossing roll is crowned, andwherein at least a portion of the perforate nips are substantiallyoriented in the cross-machine direction.
 2. The embossing systemaccording to claim 1 wherein at least a portion of each of the first andsecond embossing rolls is crowned.
 3. The embossing system according toclaim 1 wherein the crown of the embossing roll is substantiallyparabolic in shape.
 4. The embossing system according to claim 1 whereinthe crown is at least approximately 1 mil.
 5. The embossing systemaccording to claim 4 wherein the crown is at least approximately 2 mils.6. The embossing system according to claim 5 wherein the crown is atleast approximately 3 mils.
 7. The embossing system according to claim 6wherein the crown is at least approximately 5 mils.
 8. A perforateembossing roll having embossing elements wherein at least a majority ofthe embossing elements are substantially oriented in the cross-machinedirection and wherein the embossing roll is crowned.
 9. The perforateembossing roll according to claim 8 wherein the crown of the embossingroll is substantially parabolic in shape.
 10. The perforate embossingroll according to claim 8 wherein substantially all of the embossingelements are substantially oriented in the cross-machine direction. 11.The perforate embossing roll according to claim 8 wherein the crown isat least approximately 1 mil.
 12. The perforate embossing roll accordingto claim 11 wherein the crown is at least approximately 2 mils.
 13. Theperforate embossing roll according to claim 12 wherein the crown is atleast approximately 3 mils.
 14. The perforate embossing roll accordingto claim 13 wherein the crown is at least approximately 5 mils.
 15. Anembossing system for perforate embossing at least a portion of a webcomprising: a first embossing roll having embossing elements, the firstembossing roll being in communication with a first gear; and at least asecond embossing roll having embossing elements, the second embossingroll being in communication with a second gear, wherein the embossingelements of the first and second embossing rolls define perforate nipsfor embossing and perforating the web; and wherein at least a portion ofthe perforate nips are substantially oriented in the cross-machinedirection, and wherein the first gear and the second gear have aprecision rating of greater than Q-6.
 16. The embossing system accordingto claim 15 further comprising a precision hub in direct communicationwith at least one of the first gear and second gear to reducecircumferential alignment drift of at least one embossing roll.
 17. Theembossing system of claim 15 wherein the first gear and the second gearhave a precision rating of at least about Q-8.
 18. The embossing systemof claim 17 wherein the first gear and the second gear have a precisionrating of at least about Q-10.
 19. The embossing system of claim 15wherein the first gear and the second gear are pre-heat treated gears.20. The embossing system of claim 15 wherein the first gear and thesecond gear are hobbed gears.
 21. The embossing system of claim 15wherein the first gear and the second gear are ground gears.
 22. Theembossing system according to claim 15 wherein the first gear and thesecond gear are shaved gears.
 23. An embossing system for perforateembossing at least a portion of a web comprising: a first embossing rollhaving embossing elements, the first embossing roll having a firstalignment means; and at least a second embossing roll having embossingelements, the second embossing roll having a second alignment means,wherein the embossing elements of the first and second embossing rollsdefine perforate nips for embossing and perforating the web; and whereinat least a portion of the perforate nips are substantially oriented inthe cross-machine direction.
 24. The embossing system of claim 23wherein at least one of the first or second alignment means includes acollar having a keyway.
 25. The embossing system of claim 23 wherein thefirst alignment means includes an adjustable collar and the secondalignment means includes a fixed collar.
 26. The embossing system ofclaim 23 wherein at least one of the first or second alignment meansincludes scribe marks.
 27. The embossing system of claim 23 wherein thefirst and second alignment means include matched keyways.
 28. Aperforate embossing roll having embossing elements wherein at least amajority of the embossing elements are substantially oriented in thecross-machine direction and wherein the embossing roll has an alignmentmeans.
 29. The perforate embossing roll according to claim 28 whereinsubstantially all of the embossing elements are substantially orientedin the cross-machine direction.
 30. The perforate embossing rollaccording to claim 28 wherein the alignment means includes an adjustablecollar.
 31. The perforate embossing roll according to claim 28 whereinthe alignment means includes a scribe mark.
 32. The perforate embossingroll according to claim 28 wherein the alignment means includes a fixedcollar.
 33. The perforate embossing roll according to claim 28 whereinthe alignment means includes a matched keyway.
 34. A method of engagingat least two perforate embossing rolls comprising: providing a firstembossing roll having at least a portion of the embossing elementssubstantially oriented in the cross-machine direction, the embossingroll having a first collar, and the first collar having a first keyway;providing at least a second embossing roll having at least a portion ofthe embossing elements substantially oriented in the cross-machinedirection, the embossing roll having a second collar, and the secondcollar having a second keyway; bringing the first and second embossingrolls into close proximity; aligning the first and second keyways; andbringing the first and second embossing rolls into engagement.
 35. Themethod according to claim 34 wherein at least one of the first or secondcollar is an adjustable collar ring. 36-42. (canceled)
 43. A method forembossing and perforating at least a portion of a web comprising:providing a first embossing roll having embossing elements, the firstembossing roll being in communication with a first gear; and providingat least a second embossing roll having embossing elements, the secondembossing roll being in communication with a second gear, wherein atleast a predominate number of the embossing elements are substantiallyoriented in the cross-machine direction and wherein the first and secondembossing rolls define a perforate nip for embossing and perforating theweb, and wherein the first gear and the second gear have a precisionrating of greater than Q-6; and passing the web between the first andsecond embossing rolls wherein the first and second embossing rolls areconfigured and the engagement and alignment therebetween are controlledto result in an element clearance that will achieve a non-pickingclearance while achieving at least a 15% reduction in the machinedirection tensile strength of the web.
 44. The method according to claim43 wherein the first gear and the second gear have a precision rating ofat least about Q-8.
 45. The method according to claim 44 wherein thefirst gear and the second gear have a precision rating of at least aboutQ-10.
 46. The method according to claim 43 wherein the first gear andthe second gear are pre-heat treated.
 47. The method according to claim43 wherein the first gear and the second gear are hobbed gears.
 48. Themethod according to claim 43 wherein the first gear and the second gearare ground gears.
 49. The method according to claim 43 wherein the firstand second gears are shaved gears.
 50. The method according to claim 43further comprising a precision hub in direct communication with at leastone of the first gear and second gear to reduce circumferentialalignment drift of at least one embossing roll. 51-53. (canceled)
 54. Amethod for perforate embossing a web without increasing the MD/CDtensile ratio of the web comprising: passing a web through an embossingsystem, wherein the embossing system comprises a first embossing rollhaving embossing elements and wherein the first embossing roll is incommunication with a first gear, and at least a second embossing rollhaving embossing elements, wherein the second embossing roll is incommunication with a second gear, the first and second gears having aprecision rating of at least Q-6, and wherein the first and secondembossing rolls define a plurality of perforate nips for embossing andperforating the web; and wherein at least a predominant number of theperforate nips are substantially oriented in the cross-machinedirection.
 55. The method according to claim 54 further including aprecision hub. 56-57. (canceled)
 58. A method of perforate embossing aweb comprising: passing a web through an embossing system, wherein theembossing system comprises a first embossing roll having embossingelements, wherein the first embossing roll is in communication with afirst gear, and at least a second embossing roll having embossingelements, wherein the second embossing roll is in communication with asecond gear, the first and second gears having a precision rating ofgreater than Q-6, and wherein the first and second embossing rollsdefine a plurality of perforate nips for embossing and perforating theweb; and wherein the MD/CD tensile ratio of the web is not increased.59. A perforate embossing roll having embossing elements wherein atleast a portion of the embossing elements are substantially oriented inthe cross-machine direction, wherein the embossing roll is incommunication with a gear, and wherein the gear has a precision ratingof greater than Q-6.
 60. The perforate embossing roll according to claim59 wherein the gear has a precision rating of at least approximatelyQ-8.
 61. The perforate embossing roll according to claim 60 wherein thegear has a precision rating of at least approximately Q-10.
 62. Theperforate embossing roll according to claim 59 wherein the gear is apre-heat treated gear.
 63. The perforate embossing roll according toclaim 59 wherein the gear is a hobbed gear.
 64. The perforate embossingroll according to claim 59 wherein the gear is a ground gear.
 65. Theperforate embossing roll according to claim 59 wherein the gear is ashaved gear.
 66. An embossing system for perforate embossing at least aportion of a web comprising: a first embossing roll having embossingelements; and at least a second embossing roll having embossingelements, wherein the embossing elements of the first and secondembossing rolls define perforate nips for embossing and perforating theweb, wherein the first and second embossing rolls have an alignmentmeans, and wherein at least a portion of the perforate nips aresubstantially oriented in the cross-machine direction.
 67. The embossingsystem of claim 66 wherein the alignment means includes a collar havinga keyway.
 68. A method of engaging at least two embossing rollscomprising: providing a first embossing roll having perforate embossingelements substantially oriented in the cross machine direction;providing at least a second embossing roll having perforate embossingelements substantially oriented in the cross machine direction, thefirst and second embossing rolls having an alignment means; bringing thefirst and second embossing rolls into close proximity; aligning thealignment means; and bringing the first and second embossing rolls intoengagement.
 69. The method according to claim 68 wherein the alignmentmeans includes a collar having a keyway.
 70. A method of perforateembossing a web wherein at least a majority of the perforations aresubstantially oriented in the cross-machine direction and wherein thecaliper profile, Delta_(c), of the web is less than 2.